Chemistry of the Atmosphere PDF

Chemistry of the Atmosphere Learning Objectives State the composition of the Earth’s atmosphere.  Greek: atmos (vapor/steam), sphaira (ball/ globe) Modern Latin: atmosphaera Gaseous envelope surrounding the Earth 3 Troposphere Stratosphere...

Chemistry of the Atmosphere Learning Objectives State the composition of the Earth’s atmosphere.  Greek: atmos (vapor/steam), sphaira (ball/ globe) Modern Latin: atmosphaera Gaseous envelope surrounding the Earth 3 Troposphere Stratosphere Mesosphere Thermosphere (Ionosphere) Exosphere ▪ Closest to Earth’s surface (7-18 km above the equator) ▪ Most active region – where all the dramatic events of weather (rain, lightning, hurricanes) occur ▪ Contains almost 80% of the total mass of air and practically all the atmosphere’s water vapor (forms clouds and rain) ▪ Thinnest layer of the atmosphere (10 km) ▪ Temperature decreases with increasing altitude ▪ Consists of nitrogen, oxygen and ozone. ▪ 19-50 km above the equator ▪ Air temperature increases with altitude due to the exothermic reactions triggered by UV radiation from the sun. ▪ One of the products of this reaction sequence is ozone (O3), which serves to prevent harmful UV rays from reaching Earth’s surface. ▪ 30-50 km above the equator ▪ The concentration of ozone and other gases is low ▪ The temperature decreases again with increasing altitude ▪ 50-400 km above the equator ▪ Temperature increases with altitude – as the result of the bombardment of molecular O2 and N2 and atomic species by energetic particles, such as electrons and protons, from the sun. ▪ In reverse, these processes liberate the equivalent amount of energy, mostly heat. ▪ Ionized particles are responsible for the reflection of radio waves back toward Earth. ▪ ~400 km above the equator ▪ The outermost layer of our atmosphere ▪ This layer separates the rest of the atmosphere from outer space – 10,000 km thick ▪ There is a lot of empty space in between of very spread out hydrogen and helium gases. ▪ There is no air to breathe and it is very cold. ▪ The total mass of the atmosphere is about 5.3 x 1018 kg ▪ Water is excluded from this table because its concentration in air can vary drastically from location to location. ▪ Molecular nitrogen, with its triple bond, is a very stable molecule. ▪ Nitrogen fixation – the conversion of molecular nitrogen into nitrogen compounds such as nitrates. ▪ Atmospheric nitrogen fixation electrical N2 (g) + O2 (g) energy 2NO (g) (lightning) 2NO (g) + O2 (g) 2NO2 (g) 2NO2 (g) + H2O (l) HNO2 (aq) + HNO3 (aq)  ▪ Nitric acid is converted to nitrate salts in electrical N2 (g) + O2 (g) energy 2NO (g) (lightning) the soil. 2NO (g) + O2 (g) 2NO2 (g) ▪ These nutrients are taken up by plants, 2NO2 (g) + H2O (l) HNO2 (aq) + HNO3 (aq) which in turn are ingested by animals. ▪ Animals use the nutrients from plants to make proteins and other essential biomolecules. ▪ Denitrification reverses nitrogen fixation to complete the cycle. ▪ For example, anaerobic organisms decompose animal wastes as well as dead plants and animals to produce free molecular nitrogen from nitrates. Industrial Nitrogen Fixation catalyst N2 (g) + 3H2 (g) 2NH3 (g) NH3 + 2O2 HNO3 + H2O NH3 + HNO3 NH4NO3 fertilizer ▪ The cycle is complicated because oxygen takes so many different chemical forms. ▪ Atmospheric oxygen is removed through respiration and various industrial processes (mostly combustion), which produces CO2. ▪ Photosynthesis is the major mechanism by which molecular oxygen is regenerated from CO2 and water. ▪ Spectacular celestial light shows as a result of ejection of myriad electrons and protons in space during solar flares or violent eruptions on the surface of the sun. ▪ Aurora borealis – Northern Hemisphere; ▪ Aurora australis – Southern Hemisphere ▪ These electrons and protons collide with the molecules and atoms in Earth’s upper atmosphere, causing them to ionized and electronically excited. hn + N2 2N hn + N N* + e- hn + O2 O2* + e- ▪ The excited molecules and ions return to the ground state with the emission of light. ▪ An excited oxygen atom emits photons at wavelengths of 558 nm (green) and between 630 and 636 nm (red). ▪ The blue and violet colors often observed in auroras result from the transition in the ionized nitrogen molecule. The wavelengths for this transition fall between 391 and 470 nm.